This invention pertains, in general, to mixing valve arrangements and, in particular, to a mixing valve arrangement for mixing water in sanitary applications and having an electrically actuated supply valve in the hot and cold water supply lines and a preselection device.
Mixing valves of this type are well known through, for example, CH-PS No. 451 626 and DE-OS No. 23 23 841. One characteristic of such mixing valves is that sudden fluctuations of pressure in the supply mains always have an initial effect on the mixed water temperature. In particular, the mixing water temperature increases considerably at first when the pressure in the cold water supply main falls suddenly. Such a sudden fall in cold water pressure can occur, for example, when a parallel connected consumer suddenly draws off large volumes of cold water (flushing a WC etc.). When a high mixed water temperature has already been set, a sudden fall in cold water pressure can present a danger of scalding. This problem of the well known type of mixing valve is due to a certain delay in control changes in response to the altered value of the mixing water temperature. This time delay depends on the length of time it takes for the water to flow from the mixing chamber to the temperature detector, the time constant of the temperature detector - which is also increased still further by the thermal capacity of the surrounding mixing chamber - and by the time constant of the control elements. It is of course possible in principle to reduce the time constants, but this very considerably increses the cost of the temperature detector and the control elements. For this reason, the well know types of mixing valve have the main disadvantage that pressure fluctuations in the supply mains always manifest themselves as more or less large initial variations of the mixed water temperature irrespective of how the control principle is applied in detail.
It is one object of the invention to provide an improved mixing valve of the aforementioned type by considerably improving the constancy of the mixing water temperature when the pressure fluctuates in the supply mains.